This article presents the gradual liberalization of European air transport, especially its most recent problems in the case of the Single European Sky (SES). Indeed, after successfully liberalizing airlines and, to a certain extent, airports, the European Commission has embarked on the process of creating an SES. The article describes the process and the main actors. It focuses in particular on the identification of the various actors' interests, and explains the current gridlock of the SES as a result of conflicting objectives among the main players, which include, among others, the member states and the European Commission. A way out of this gridlock may reside in a novel approach to unbundling different types of services, and introducing competition in some of these services.